The present invention relates to the application of high gradient magnetic separation (HGMS) to the process of separation and isolation of materials labeled magnetised particles.
A HGMS system consists of a filter of fine magnetisable wires placed in a strong magnetic field. This causes high gradient magnetic fields to be produced around the wires, allowing the capture of even very weakly magnetic particles upon the magnetised wires.
HGMS was first proposed during the search for the elusive magnetic monotone, and its first industrial application was the removal of staining iron from clay. Since then, numerous other industrial applications for HGMS have been developed, including mineral benefication, sewage and industrial effluent treatment, and nuclear fuel reprocessing. The first application of HGMS to the separation of human cells took place in 1975, when it was shown that erythrocytes (red blood cells) could be retained on a HGMS filter (Melville, D., et al., Nature 255:706, 1975). Because almost all human cells are relatively nonmagnetic in aqueous media, the desired cells must be specifically labeled with a magnetic material in order for HGMS to be used to its full potential. Typically, a magnetic material is attached to an antibody which identifies and allows the magnetic material to attach to the desired cell.
There are potentially a large number of applications of HGMS to the separation and isolation of biological cells. One example of this is in the treatment of leukaemia, whereby cancerous cells are separated and removed from the bone mirror of the patient, or alternatively, the pluripotent stem cells of the bone marrow (CD34 positive cells, known as the father cells of bone marrow) can be separated and purified.
There have been several attempts to apply HGMS to the separation and isolation of magnetically labelled CD34 positive cells, although the recoveries and purities achieved have been undesirably low (For example, see Kato, K., and Radbruch, A., Cytometry 14:384, 1993). Typically, attempts have employed an HGMS filter which consists of a random or semi-random array of stainless steel wire wool packed loosely into a column located in a strong magnetic field (Miltenyi, S. et al., Cytometry 11:231, 1990; Molday, R. S. and Molday, L., FEBS. Lett. 170:232, 1984; Kato, K and Radbruch, A., supra; Kemshead, J. T. in Hematotherapy 1:35, 1992; and Kemshead, J. T. in Bone Marrow Processing and Purging, 293, Gee, A.P. Ed., C.R.C. Press, Inc., Boca Raton, Fla., 1991).
Existing HGMS cell separation systems have difficulty in separating cell suspensions which exhibit the following characteristics: the desired cells have low and variable antigenic sites on their surfaces so they do not form a well defined labelled population, the desired cells are in variable and low abundance in the heterogenous cell population, highly adhesive cells which will adhere to any surface are present, and total cell numbers for separation are large (i.e. &gt;10.sup.9). Separation of CD34 positive cells from bone marrow is an extreme example of suspensions exhibiting these characteristics.
Therefore, there is a need for an improved cell separation system which addresses the problems associated with the prior art.